I scratched for this error for more then 6 months i was unable to trace this error then one day i just removed the update panel and come to know that there was an error at server side code .
so something went wrong and its out of scope of script manager.
as I also visited many links related this errors,even then unable to solve by those details as it was not clear what causes this error.
So i am posting here the Solution for this Error.
Just remove the updated panel and debug you will find error and fix that error and then put update panel again.
thanks-Hope this will help to some one facing the issue